Semiconductor processing tools often include components designed to distribute process gases in a relatively even manner across a semiconductor substrate or wafer. Such components are commonly referred to in the industry as “showerheads.” Showerheads typically include a faceplate that fronts a plenum volume of some sort. The faceplate may include a plurality of through-holes that allow gas in the plenum volume to flow through the faceplate and into a reaction space between the substrate and the faceplate (or between a wafer support supporting the wafer and the faceplate). The through-holes are typically arranged such that the gas distribution across the wafer results in substantially uniform wafer processing.